1. Field of the Invention
The present invention relates to lightweight armor and high impact structures. More particularly, the invention relates to lightweight armor, composite structures comprising an ionomer and an aramid and/or linearly crystallized polyethylene fiber structure.
2. Prior Art
There is a continuing need to improve the stopping power of lightweight composite armor which is used for spall shields, helmets and personal ballistic vests and armor. Layers of woven Kevlar (aramid) is the most common ballistic shield used for personal protection today. Spectra (linearly crystallized polyethylene) is also being evaluated with success for these same applications. As larger projectiles or fragments come into contact with these structures, the yarns go into tension and the load is transferred along the axis of the fibers and filament yarns. The projectile is decelerated at this moment as long as the yarns of the ply hold. As these yarns break the load is transferred to the fabric of the next ply and so on.
In order to improve the stopping power of these woven (or even nonwoven) structures, some means is needed to add greater resistance to the deformation/penetration ability of the projectile and to prevent the projectile from slipping past the yarn. An optimum fabric resin composite contains about 35% resin. If this same amount of resin could be added to a high strain-type ballistic fabric such as Kevlar 29 or Spectra in a manner that is reinforcing and aids in the deceleration of the projectile, then an enhanced lightweight protective ballistic armor can be formed.
The problem is, up to now, only rigid-type resins (thermosets) have been used with these high strain, high tenacity woven fibers. These resins being rigid, clamp or stop the high strain fiber from going into tension, thereby concentrating the impact load on a smaller cross sectional area of fabric. Therefore, the ability of the ballistic fabric to stop projectiles is lessened with rigid resins.
It is common practice to add poorly bonding resins such as phenolic or modified polyester to these high strain ballistic fabrics in order to form composites in which the resin does little more than keep out water. In addition, often a nonbonding rubber latex is added to enhance nonbonding to the high strain, high tenacity fiber (Kevlar), in order that the high strain fiber breaks free of the composite matrix and goes into tension along its length, immediately and thus carrying the impact load over as large an area as possible, increasing the stopping power of the ballistic fabric stack in the weak composite form.
Ideally, it would be a significant improvement if the matrix resin had about the same or faster elastic response properties to high velocity impact (ballistic). Then the impact load is absorbed both by the matrix and by the high strain fiber simultaneously and the load is distributed laterally (over the widest area) to the greatest extent. In this latter situation, the matrix resin is absorbing part of the load and yet not causing a lessening of the Kevlar to go into lateral tension and thereby involving the maximum amount of fibers in the deceleration process. The resin itself will help transfer the load from fiber to fiber. In this situation, there are two criteria that must be met: (1) the matrix resin must respond as fast or faster than Kevlar to ballistic impact and begin to stretch and spread the load immediately on impact, and (2) the resin must form a good bond to the high strain fiber for maximum results. This is contrary to the commonly used design criteria for these lightweight composites.
Smith U.S. Pat. No. 4,732,803, which is incorporated herein by reference, discloses an armor structure which can be utilized together with the present invention.
Clausen U.S. Pat. No. 4,186,648, et al, which is incorporated herein by reference, describes an armor wall structure comprising a plurality of woven fabric laminates of polyester resin fibers arranged and supported in and by a resinous matrix with a filler of particulate metal abrading material and woven fabric laminates. This reference discloses abrading material which can be used in the present invention.
Donovan U.S. Pat. No. 4,574,105 discloses penetration resistant textile panels with plies of nylon and Kevlar.
Seigfried U.S. Pat. No. 4,468,499 et al, which is herein incorporated by reference, discloses chemically blended thermoplastic interpenetrating polymer network compositions.
Rees U.S. Pat. No. 3,471,460which is herein incorporated by reference, discloses ionomers which can be utilized in the invention.
Smith U.S. Pat. No. 4,732,944which is herein incorporated by reference, discloses amine modified ionomers which may be used in the present invention.
There are many lightweight materials which have high strength and elasticity but do not respond well when subjected to impact velocities over 2000 ft/sec. High modulus and high strength materials are usually brittle and crack or notch sensitive. Once damaged, these high modulus and high strength materials lose a great deal of their stopping power or impact strength due to crack sensitivity.
Elastomeric materials are not usually crack or damage sensitive but can be readily penetrated at high impact velocities.
Chopped glass fibers and most other material fillers are known to usually increase the impact resistance of resins with which they are compounded because they act as stress concentrators. However, glass fibers and fillers alone further tend to embrittle ductile and semiductile polymers. Addition of plasticizers and energy-absorbing constituents such as rubbers tend to overcome the embrittlement sensitivity or crack propagation but decrease the energy dissipation away from the lateral direction and decrease penetration resistance per unit area.
It is desirable to provide armor which can stop "needle penetration"; that is, penetration by sharp pointed objects such as ice picks, shrapnel, high velocity small caliber bullets, and the like.
The use of woven fiber structures alone has been ineffective in providing enhanced stopping ability without a major increase in mass or thickness for stopping high impact small cross section projectiles such as needles, ice picks, or small caliber bullets.
In the specification and claims the term "ionomer" or "ionomer resin" mean an extrudable resin comprising ionically crosslinked ethylene-methacrylic acid and ethylene-acrylic acid copolymers. Properties which distinguish these ionomer resins from other polyolefin heat-seal polymers are tear resistance, abrasion resistance, solid-state toughness and resistance to oil-fat permeation. The starting ionomer resins are generally available as either a partially neutralized sodium or a zinc ionomer, and are available in a wide variety of grades. However, the esters or the non-neutralized acid form of the resin are also adaptable to the present invention.
Various grades of ionomer resins are available for extrusion coating and film extrusion. A very wide variety of partially neutralized ionomer resins are manufactured by E. I. DuPont de Nemours and Company under the registered trademark "SURLYN" or by Dow as "PRIMACORE".
One ionomer or ionomer resin of the invention is obtained by combining a copolymer of ethylene-methacrylic acid or ethylene-acrylic acid and a polyamine which contains at least one R--CH.sub.2 --NH.sub.2 group, and the R may contain: (--CH.sub.2 NH.sub.2).sub.x ; (--NH.sub.2).sub.x ; or (R'R"NH).sub.y, where x=1 or more, and y=0 or more. R' and R" may be any organic groups. The preferable structure of the diamine is: EQU NH.sub.2 CH.sub.2 --(R)--CH.sub.2 NH.sub.2 ( 1)
where R contains from one to twenty five carbon atoms; R may be aliphatic, alicylic or aromatic; and R may also contain: EQU --CH.sub.2 OCH.sub.2 --; (2) ##STR1##